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The Journal of Neurophysiology Vol. 87 No. 5 May 2002, pp. 2287-2296
Copyright ©2002 by the American Physiological Society
1Department of Pharmacology and 2Department of Anatomy, College of Veterinary Medicine and School of Agricultural Biotechnology, Seoul National University, Suwon 441-744, Korea
Han, Seong Kyu,
Wonee Chong,
Long Hua Li,
In Se Lee,
Kazuyuki Murase, and
Pan
Dong Ryu.
Noradrenaline Excites and Inhibits GABAergic Transmission in
Parvocellular Neurons of Rat Hypothalamic Paraventricular
Nucleus. J. Neurophysiol. 87: 2287-2296, 2002. Noradrenaline (NA) is a major neurotransmitter
that regulates many neuroendocrine and sympathetic autonomic functions
of the hypothalamic paraventricular nucleus (PVN). Previously NA has been shown to increase the frequency of excitatory synaptic activity of
parvocellular neurons within the PVN, but little is known about its
effects on inhibitory synaptic activity. In this work, we studied the
effects of NA (1-100 µM) on the spontaneous inhibitory synaptic
currents (sIPSC) of type II PVN neurons in brain slices of the rat
using the whole cell patch-clamp technique. Spontaneous IPSCs were
observed from most type II neurons (n = 121) identified by their anatomical location within the PVN and their
electrophysiological properties. Bath application of NA (100 µM)
increased sIPSC frequency by 256% in 59% of the neurons. This effect
was blocked by prazosin (2-20 µM), the
1-adrenoceptor antagonist and mimicked by
phenylephrine (10-100 µM), the
1-adrenoceptor agonist. However, in 33% of
the neurons, NA decreased sIPSC frequency by 54%, and this effect was
blocked by yohimbine (2-20 µM), the
2-adrenoceptor antagonist and mimicked by
clonidine (50 µM), the
2-adrenoceptor
agonist. The Na+ channel blocker, tetrodotoxin
(0.1 µM) blocked the
1-adrenoceptor-mediated effect, but not the
2-adreonoceptor-mediated one. Both of the stimulatory and inhibitory effects of NA on sIPSC frequency were observed in individual neurons when tested with NA alone, or both phenylephrine and clonidine. Furthermore, in most neurons that showed
the stimulatory effects, the inhibitory effects of NA were unmasked
after blocking the stimulatory effects by prazosin or tetrodotoxin.
These data indicate that tonic GABAergic inputs to the majority of type
II PVN neurons are under a dual noradrenergic modulation, the increase
in sIPSC frequency via somatic or dendritic
1-adrenoceptors and the decrease in sIPSC
frequency via axonal terminal
2-adrenoceptors
on the presynaptic GABAergic neurons.
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